Exterior components of watches and accessories are required to have both a color tone that is an ornamental factor and an abrasion resistance that is a functional factor. Gold is most suitable for this requirement. For instance, conventionally, the material of gold is processed, or a gold plating coating layer is formed on other metals. When a corrosion resistance is not required in particular, even a coating layer of 1 micrometer or less can achieve a purpose of displaying a gold color. However, a high resistance to sweat, water vapor, etc. is required for watch cases, watch bands and accessories, and therefore the gold plating layer should be at least 10 micrometers in thickness.
However, gold is an extremely expensive metal, which limits exterior components to which a gold coating layer having a large thickness can be applied. Consequently, a coating layer using a reduced amount of gold is required. Moreover, the hardness of gold is approximately 200 Hv, and gold has a low mar resistance. Accordingly, gold is easily flawed disadvantageously when a wristwatch or an accessory is carried. Therefore, it is desired that a gold coating layer that is inexpensive and displays sufficient functions is developed.
As a result, coating layers made of titanium nitride and gold or a gold alloy by dry plating technology such as ion plating or sputtering are proposed (see Patent documents 1 to 3 for instance). Consequently, a gold coating layer that has an excellent corrosion resistance, an excellent abrasion resistance, and a thin film thickness can be formed at a low cost. For the coating layer made of titanium nitride and gold or a gold alloy, an adhesion property to a base metal layer made of titanium or titanium nitride is improved as compared with a conventional gold plating coating layer. However, the adhesion property is still insufficient. In particular, when the film thickness of a coating layer made of titanium nitride and gold or a gold alloy is extremely small, the coating layer is easily peeled disadvantageously.
Moreover, an exterior component is disclosed in which a gold coating layer is composed of two layers of for example a titanium nitride layer and a gold or gold alloy layer (see Patent documents 1 and 2). This gold coating layer is described to have excellent mar resistance and abrasion resistance. However, because the color tones of the titanium nitride layer and the gold or gold alloy layer are different, abrasion or flaws on the surface of the gold coating layer are conspicuous disadvantageously.
Patent document 1: Japanese Patent Application Laid-Open Publication No. 54-2942
Patent document 2: Japanese Patent Application Laid-Open Publication No. 58-104176
Patent document 3: Japanese Patent Application Laid-Open Publication No. 60-67654
The present invention has been made in order to solve the above problems of the conventional art. An object of the present invention is to provide ornaments having a gold coating layer that is inexpensive and displays sufficient functions, and processes for producing the ornaments.